Methods for obtaining corn oil from milled corn germ (e.g., dry milled corn germ), involving adding water, at least one acidic cellulase, at least one acidic protease, and optionally at least one phytase to milled corn germ to obtain corn oil.
Dry milled corn germ is a coproduct of the dry milling of corn, the process used to make food grade corn meal (with germ removed to extend the shelf life), corn germ, grits (also called flaking grits when used to make corn flakes), and corn bran, most of which are used for ingredients for breakfast cereals and other food products (Duensing, W. J., et al., “Corn Dry Milling: Processes, Products, and Applications, IN Corn Chemistry and Technology, Second Edition, P. J. White and L. A. Johnson, Eds., American Association of Cereal Chemists, Inc., St. Paul, pp 407-448, 2003). Before dry milling the corn is tempered by adding a small amount of moisture (˜20%) and then the kernels are gently milled and the three major fractions (endosperm, germ, and bran) are separated by mechanical processes such as aspiration and sieving. This germ contains most of the edible oil found in the corn kernel, and the concentration of oil in the germ is about 16-22% on a dry weight basis. This type of corn germ along with the type of germ produced by the corn wet-milling industry (wet-mill germ) are the source of practically all of the commercial corn oil produced and sold in the world. Most commercial corn oil (about 90%) is produced by hexane extraction and/or mechanical pressing of wet milled corn germ. Corn oil and all other types of edible oils are currently selling at high prices due to the worldwide demand for oils for food, feed, and biofuels production. Recently, producers of fuel ethanol from corn have realized that the oil from their incoming corn feedstock, which traditionally was not recovered and was therefore sold as a component of the distillers dried grain with solubles (DDGS) coproduct, would be a value-added coproduct if it could be economically collected. One process for doing this involves the use of the dry milling process to recover the corn germ from the corn kernel prior to sending the rest of the kernel through the fuel ethanol production process. While this would provide ethanol facilities with an oil-enriched germ, a pressing and/or extraction process is also needed to recover the oil to economically benefit from the germ's full value. Due to the high capital cost and significant regulatory and safety considerations, building a hexane extraction facility is not cost effective for one ethanol plant. For that reason, we have been developing simpler processes based upon “green” aqueous enzymatic oil extraction (AEOE). We previously reported an aqueous enzymatic extraction process to extract corn oil from dry fractionated corn germ using an acidic cellulase and then using an alkaline protease, but both enzymes were used at very high and uneconomical concentrations, 95 kg cellulase/MT germ (DWB) and 95 kg protease Alcalase/MT germ (DWB) (Moreau, R. A., et al., J. Am. Oil Chem. Soc., 86: 469-474 (2009)). The process also required separate reaction times at different pH values to accommodate an acidic cellulase and an alkaline protease.
We have now been able to reduce the levels of enzymes and make the aqueous enzymatic oil extraction process for milled corn germ (e.g., dry milled corn germ) simpler and more economical. This included the use of an acidic protease (for the first time), which could operate under the same pH and conditions as the acidic cellulase and optionally the use of low levels of accessory enzymes, such as phytase, to further improve the process.